Substance abuse remains a critical national problem exacerbated by the fact that treatment regimens are frequently unsuccessful. Providing specific treatment for psychiatric comorbidities may decrease the treatment relapse rates. This study will determine the prevalence of Attention Deficit Hyperactivity Disorder (ADHD) in a representative randomly selected sample of substance abusers entering inpatient drug treatment in three treatment centers. Further, the prevalence of associated conduct disorder, the age of onset of substance abuse, primary drug used, and the severity of substance abuse will be described in the substance abusing and in the ADHD-substance abusing subgroups. Finally, the predictive validity of three self-report screening instruments for ADHD in this population will be determined. 250 subjects (50% women, 28% African-American) will complete the screening instruments and be evaluated by an in-depth interview using the Structured Clinical Interview for DSM- III-R, the Addiction Severity Index, and a clinical evaluation for ADHD. Interviews will be administered by trained psychologists. Analysis will describe and compare subject subgroups (substance abuse with and without ADHD) on the above variables. Discriminant function analysis will determine the predictive validity of the three self-report instruments. Results will report the prevalence of ADHD among substance abusers and may be supportive of developing an intervention trial of ADHD treatment concurrent with substance abuse treatment in those with the dual diagnosis of ADHD and substance abuse.